Organic accelerators have long been used to reduce the cure time of sulfur vulcanized elastomer compounds. Nitrogen-bearing materials in particular can dramatically affect the rate of cure and are utilized today in practically all commerical recipes. Examples of these materials include the various well known thiazoles and sulfenamides, thiocarbamates, thiurams and certain thioureas. It has also been known that certain fatty acids, which are present in the non-hydrocarbon constituents of natural rubber have an influence on the cure rate.
Heretofore, however it has not been known to use metal salts as vulcanization accelerators. While certain metal salts are sometimes added to compounding recipes for other purposes, for example to promote rubber to metal adhesion, the recipes invariably also contain one or more of the conventional accelerators recited above. It has been found feasible and it is the primary aspect of this invention, to eliminate the use of conventional accelerators through substitution of metal salts in compounding recipes.
Prior art usage of metal salts appears in British Pat. Nos. 993,045 and 1,389,800 and European Pat. Application No. 0031398. The British patents utilize conventional prior art accelerators and thus are not pertinent. The European Patent Application contains, in addition to a conventional accelerator, a rosin-derived resin to obtain a result which is nonanalogous to the instant invention. Thus, none of these prior art disclosures recognize that metal salts in sufficient quantities can be used to accelerate sulfur vulcanization.